My macro to bold the first three characters of a cell works great but
I am struggling with enhancing the macro to automatically repeat for
the entire column "C" instead of running it cell by cell. Ideally,
the macro would run on open, but I'll settle for running it on
command.

Any help is greatly appreciated!

Dim StartChar As Integer
Dim BoldLen As Integer
StartChar = 3
BoldLen = 5
ActiveCell.Characters(StartChar, BoldLen).Font.Bold = True